Many of industrial reactions are carried out in a mixing tank type reactor using solid catalyst slurry and contacting liquid with a reactive gas, such as hydrogen or ammonia, in the presence of the catalyst to allow them to react. After the end of the reaction, generally, the catalyst is removed with filtration to collect the reaction product.
However, a slurried catalyst has problems in safety, increase in waste material, operability and productivity. For example, there are such problems that many of catalysts are spontaneously combustible and powder and slurry catalysts must be handled with care, and that the catalyst must be removed by filtration etc. in order to collect the reaction product thereby leading to complex facilities and operation.
As a process that requires neither a mixing operation by stirring or gas bubbling nor filtration separation of a catalyst, there can be mentioned a fixed-bed system. As to forms of a catalyst for use in the fixed-bed system, a molded catalyst of a pellet shape, noodle shape, or tablet shape has been well known conventionally. By subjecting powdery material having a catalyst activity to molding processing by such method as compression or extrusion into the above-mentioned form, a construction having an infinite number of fine pores therein is formed to satisfy both of the catalyst configuration and great surface area. For example, it is disclosed in JP-A 6-211754.
According to the reaction system, such problem as handleability of the catalyst and waste material can be solved, but there are many reactions to which the system can not be applied. For example, there were such instances that temperature control was troublesome in reactions accompanied with absorption or generation of heat, and that uneven liquid-gas distribution in a reactor sometimes resulted in an insufficient reaction percentage or many side reactions caused by local concentration gradient.
In tertiary amination reaction, when trying to obtain reaction product at a high reaction percentage using the molded catalyst described in JP-A 6-211754, no small amount of undesirable side products are generated. As the side product, in addition to wax or an aldol condensate generated caused by a side reaction of alcohol as the raw material, there can be mentioned ammonia generated due to disproportionation of primary or secondary amine and tertiary amine as side product from primary or secondary amine. Various improvements have been carried out for practicing the technique highly selectively while suppressing these side products.
In JP-A 2003-176255 a reactor in which a catalyst metal is adhered on the surface of monolith is disclosed. In the reactor, such advantage is noted that, in a hydrogenation reaction between a gas and liquid, material transfer is accelerated compared with a fixed-bed packed reactor of a conventional type, because the pressure drop of the reactor is small and the velocity of the gas and liquid can be made large. However, although a reaction of a compound containing a nitrogen atom is intended, only such instance is expressed clearly as a reaction according to a simple mechanism such as hydrogenation. Examples disclosed in addition to this aims to limited applications such as, mainly, hydrogenation reaction.
JP-A 2004-526032 discloses a gas-liquid reaction method having a process of running and transferring a gas-liquid feed flow in a monolithic structure catalyst bed, wherein the liquid in the feed fluid is run and transferred through the reaction path at a running liquid superficial velocity in a range of 0.01-10 cm/s, and the gas is run and transferred at a gas:liquid volume ratio G:L in a range of gas of 1-4000 gas standard state liter/liquid liter. In the document, there is described that, compared with various research results reported in conventional documents in which a reactor is operated, generally, at a comparatively high liquid superficial velocity (e.g., 30 cm/s) and a comparatively small gas/liquid ratio (e.g., 0.5 V/V) in order to maintain so-called Taylor flow conditions in a honeycomb passage, the method can easily achieve one pass inversion percentage of more than 50% on an industrial scale whether or not the Taylor flow is maintained. However, the conditions in the case where a reaction system is not specified is only means for trying to gain staying time in a catalyst bed for the purpose of attaining a design suitable for use in a single-pass reactor system. In AIChE Journal, 36, 746 (1990) cited in JP-A 2004-526032, there is already disclosed such experimental conditions as, in hydrogenation reaction of thiophene/cyclohexane with a CoMo/alumina monolithic catalyst, a liquid superficial velocity of 3.5 cm/s or less (the average of gas-liquid superficial velocity is 3.5 cm/s or less) and a gas-liquid ratio of 15 standard state litter/liquid litter or more (a gas feed rate of 3 standard state litter/h or more, a liquid feed rate of 200 mL/h or less). Further, in Ind. Eng. Chem. Fundam., 23, 82 (1984) such experimental conditions are adopted as a liquid superficial velocity of around 1.2 cm/s and gas/liquid ratio of around 3 V/V in hydrogenation reaction of nitrobenzoic acid with a monolithic palladium catalyst.